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Edexcel S2 - 27th June 2016 AM

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We know X represents the correct answer, so by logic, the amount of wrong answers is 20-X

S represents the final score, which will obviously be the amount he gets - amount he loses

So, each correct is 4 points, so it's 4X - 1(20-X)

Which = 5X-20

Because 1 point's lost for a wrong answer

I don't understand, how did you get 4X-1?

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Reply 621

Christop

Just got 48/75 on June 2014

This exam will be my ruin

Reply 622

Fedoras

Hey SeanFM I came across this thread just now and honestly I wish I had bumped into it earlier! Just wanted to say thanks a lot for all the help you are giving as I also had problems with some questions I see on the thread, but it makes sense now with yours and others' explanations. I appreciate you taking time out your day (meh, well night) to help us :smile:

And good luck everyone - hopefully we will score high marks on S2!

Reply 623

Supermanxxxxxx

Original post by Christop

Just got 48/75 on June 2014

This exam will be my ruin

I just managed to get 59/75 on June ial 2014 still need to do so many more papers

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Reply 624

undercxver

Alrighty guys, I'm off to bed. Good luck to you all, believe in yourself and you will smash it!

I'm guessing this is your last exam so enjoy it while you can. :lol:

Reply 625

кяя

GUYS HELP

So we reject the null hypothesis of p or the mean lies outside the critical region right? If we reject the null hypothesis what does it mean? That the company's claim is justified?

I'm so confused :frown:

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Reply 626

undercxver

This is a joke guys. I'm still awake. Can't sleep!

Original post by кяя

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What question are you looking at?

Have you watched the ExamSolutions videos on hypothesis testing?

Reply 627

кяя

Original post by undercxver

What question are you looking at?

Have you watched the ExamSolutions videos on hypothesis testing?

Just any question in general. Yes I've watched all the videos but I still can't grasp the idea.

I guess I'll just guess

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Reply 628

undercxver

Original post by кяя

Just any question in general. Yes I've watched all the videos but I still can't grasp the idea.

I guess I'll just guess

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Okay I'll try to sum this up as best as I can.

You reject the null hypothesis which is like an assumption made, but to prove if this assumption is right or not you do hypothesis testing.

You reject the null hypothesis if its not the null hypothesis. This could be a one tail test (say this is a binomial distribution question) p>___ (this is upper tail) and p<___ (this is lower tail. Also you can have the two tail test where p≠___. You need to choose the type of tail test depending on what the question is asking you. Sometimes they give this to you.

Anything else you need help with?

I feel the introductory videos for the hypothesis testing by the ExamSolutions dude really break it down. Maybe watch that video a couple of times, it took me ages to understand it.

Reply 629

Apolexian

Original post by кяя

Just any question in general. Yes I've watched all the videos but I still can't grasp the idea.

I guess I'll just guess

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Usually you reject/accept depending on your hypothesis and significance level.
For example lets say there is a company who is saying that the probability of their product working is 80% and they tested a sample of 100 products, out of which 62 worked. Stating hypothesis test the companies claim.

Since their is a p and n we know that X is distributed binomially
We want to test the claim that " the probability of their product working is 80%", so logically our null hypothesis would be Ho: p=0.8 , this one is always easy to get, the null you have to read the question in context, but lets say our null is H1: p<0.8 ( so the probability of the product working is less tham the claim). And lets say the siginficance level is 5% (so 0.05).
We will (after stating both hypothesis) need to fine the probability of our variable X being less than or equal to 62 ( depending on question we may need to find the probability of it being more than or equal to 62, its very important to read the question). Using the tables or formulas you find this probability, Now compare it with the significance level. In our case if the probability is less than 0.05 we find the value significant and reject the null, meaning the probaility is actually less than 0.8. If we do not reject the null, then there is enough evidence to support Ho, meaning we assume that p=0.8. Since the companies claim is that p=0.8, depending if we reject or accept we support or deny the claim, logically then if we reject Ho then we deny the claim, if we support Ho we accept the claim.

Reply 630

Apolexian

Original post by кяя

Just any question in general. Yes I've watched all the videos but I still can't grasp the idea.

I guess I'll just guess

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https://www.youtube.com/watch?v=KJFCX9aIOhE

Reply 631

L'Evil Wolf

What is the formula for variacne is ti

Do we say that the variance formula is :frown:

Sigma x^2 / n ) - (sigma x / n)^2

Reply 632

jshep000

Original post by L'Evil Wolf

What is the formula for variacne is ti

Do we say that the variance formula is :frown:

Sigma x^2 / n ) - (sigma x / n)^2

(X^2)/N - ((x)/(n))^2

Reply 633

L'Evil Wolf

Original post by jshep000

(X^2)/N - ((x)/(n))^2

are N and n different?

Thanks

Reply 634

jshep000

Original post by L'Evil Wolf

are N and n different?

Thanks

nah my caps button just messed up basically its x^2 / n minus the (mean)^2

Reply 635

L'Evil Wolf

Original post by jshep000

nah my caps button just messed up basically its x^2 / n minus the (mean)^2

thanks good luck for the exam

Good luck everyone!!

For uniform distribution and p.d.f., Is P(X=x) always zero? Why? Doesn't the graph have a respective y value for all x?

Reply 638

math42

Original post by pinksmartiee

For uniform distribution and p.d.f., Is P(X=x) always zero? Why? Doesn't the graph have a respective y value for all x?

Yeah this is true for continuous random variables. Think of it them as like a measurement, for instance with a ruler. You might have a very precise ruler that allows you to know something's length to a high degree of accuracy but there is still a measure of uncertainty. So you can know that, where X is length, a - delta < X < a + delta for instance, where delta is just a very small number, but you can't pinpoint it and say X = a.

Reply 639

khaleesi98

Original post by pinksmartiee

For uniform distribution and p.d.f., Is P(X=x) always zero? Why? Doesn't the graph have a respective y value for all x?

Probability is the area under the graph e.g. P(a<x<b) is the area between a and b. If you're trying to do P(X=x) then the width is 0 so the area is 0.

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